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Monday, October 11, 2010

Impressive HB in Russian

Bruce Baxter, provided links via one of his notes on the "Homebrew_PCBs" list server that was very impressive, video narrative is Russian but, Homebrew is a universal language.

With permission, a copy of Baxter's original note/email text is provided here (normally, I would just link to the original note, but it contains many links that I want to capture here for future reference)

While Looking at your reference, I noticed the statement" "There is still everyone's favorite FGK-120".

I couldn't find any availability of the product in the US. However, from the photos of the Chinese marketers, I recognized it as a Tamerica LP-120 which is sold in the US for about $51. This is the laminator I use and it does a great job with toner transfer.

Although this is a bit off topic, The second video discusses a PCB tinning method using citric acid, boiling water and some metallic particles called alloy Rose. The process seems quite simple without any bad chemicals. A bit of searching identified alloy Rose as a low temperature solder (203-212 deg F) called Rose's metal or Rose's alloy composed of bismuth, tin and lead,

The McMaster-Carr product seems to have the lowest melting point (203 deg F) with

Bismuth = 52.5%

Tin = 15.5%

Lead = 32.0%

wikipedia-Solder has this to say about Bismuth alloys,

"Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn16Pb32Bi52 with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability."

Based upon this, Rose's alloy may of limited utility for DIY PCB tinning. However, With the low melting temperature, it seems almost as useful as polymorph (friendly) plastic for prototyping parts .

Baxter

UPDATE:

I have tried to obtain Bismuth from locations around Seattle, so far I have NOT located a source - Green (no-lead) Sinkers and Green Shotgun Shot has not sold well enough to stock it locally. Because of it's weight, an Internet purchase may be prohibitive for medium (e.g., 10lbs) quantities.